1. Field of the Invention
The present invention relates generally to strippable adhesive tapes for sealing carton flaps or joints during manufacture or after filling of the cartons. The purpose of the invention is to provide a tape that can be removed easily, leaving the joint entirely free, by a simple stripping operation, so that the contents of the carton may be reached, or so that the carton itself may be readily dismantled for flat packing to be recycled or destroyed.
2. Description of the Prior Art
In the prior art are many strippable sealing tapes. However, there has long been the need of an inexpensive strippable lightweight tape fulfilling standard requirements for securing a carton in manufacture or closing, yet strippable in a manner releasing the carton sides or flaps for instant access to or removal of the contents.
Among prior strippable tapes are laminated or single layer tapes using pull-cords, such as shown in the Stark U.S. Pat. No. 3,504,844, wherein a cord is secured medially along the bottom face of a reinforced laminated tape. The cord complicates reeling of the tape, since it causes a medial ridge in the roll, accumulating with each convolution. The tape is difficult to remove, since the cord must be located, and the draw force applied essentially to it rather than to the tape itself, if the joint is to be separated. Other like tapes have used multiple draw cords or fibers, with similar problems.
Another prior art type of strippable tape is that providing a draw-strip of strong tape material. As with the pull-cord tapes, the draw-strip tapes require an additional element, adding cost. Draw-strip tapes also have the disadvantage that the draw-strip is normally not glued to the carton, and so weakens the overall strength of the tape by leaving a band along the carton panels or flaps that is unsecured. This is a serious disadvantage in that it not only reduces the transverse strength of the joint, but also permits a slippage of the joint edges in kneading type movements that shortens its life. Some non-strippable tapes, such as in the Angier U.S. Pat. No. 2,283,349 have this last disadvantage without having a stripping feature.
A further prior type of tape simply employed perforations through the tape, so that a medial strip can be pulled out. If the medial strip is glued down, it cannot readily be pulled off. If it is not glued down, it weakens the joint. If the tape is fiber reinforced, the perforated strip is largely ineffective.
In using many prior art tapes, even where they have a bottom lamination of low internal bond, that can delaminate to permit stripping, the lack of a clean separation of the stripped joint requires either a blow on the panels to complete their separation, or as is the more frequent practice, the use of a sharp razor blade to do so. Any such practice requires added labor and cost; and the use of the razor blade too often results in damage to the contents.
The present invention overcomes the foregoing problems. It incorporates a strong upper layer, that may be reinforced with fibers. This layer provides adequate strength to the joint. By having a bottom layer of low internal bond material, that is firmly united with the upper layer throughout the extent of the upper layer, with adhesive throughout the under side of the bottom layer, the strong upper layer is bonded to the box panels throughout its width, and all the way across the tape and the joint. By virtue of the medial slit along and through the bottom layer, which may be only of knife-blade width, the stripping of the tape, with internal delamination of the bottom layer, leaves the two lateral portions of the bottom layer separately on the two sides of the joint, with the joint completely separated.
An important feature of the present invention is that it does not seriously reduce the strength of the joint. Preferably it is used with fiber reinforcement in the tape, which may be between the upper and bottom layers. Since the slit is so narrow, and the adhesive extends from the edges of the tape to the strip, the fiber or other strength component or components, do not "work" as twisting or distorting forces are applied to the carton. The strength components can easily be made strong enough to provide adequate strength, either transversely or longitudinally of the tape.
If desired, the slit through the bottom layer may be extended laterally, by being made zig-zag or the like. This gives tolerance in applying the tape to a joint, as the slit will be effective to separate the joint upon stripping, even if the tape is laterally misplaced. However, usually this is unnecessary, as the joints have sufficient tolerance, and a single straight slit is in itself a visible marker that can be aligned with the line of junction of the box panels.
The present tape can be used to seal carton closure flaps. It also can be used in manufacture of cartons, to seal edges. It makes such cartons reusable or recyclable, since the customer can quickly strip the tapes and revert the carton to a flat state for either shipment back to the factory for retaping and refilling, or shipment to a reprocessing plant to recover the paper.
The present tape is relatively inexpensive, easily made, and overcomes the problems of strippable tapes heretofore existing. It is described herein in connection with closing cartons, especially corrugated boxes, but its range of uses is much greater, as will be understood.